1. Field of the Invention
The present invention relates to a radio-link continuity keeping equipment which is used in a cellular telephone mobile station to keep a radio-link continuity when a power supply battery is exchanged during conversation on the telephone.
2. Description of the Related Art
FIG. 4 shows an arrangement of a prior art cellular telephone mobile station which keeps a radio-link with use of an electronic power supply switch when a battery is exchanged during conversation through the telephone. FIG. 5 shows a flowchart for explaining the operation of the radio-link keeping equipment.
In FIG. 4, a main CPU (central processing unit) 1 performs general control over the mobile station, and a secondary CPU 2 controls a display 21, a key-input unit 22 and an electronic power supply switch 35 and so on. More specifically, the main CPU 1 controls an RF (radio-frequency) transmitter, an RF receiver, the secondary CPU 2, a channel supervisory signal receive/send circuit 11, channel selector 12, an RF transmitter operation switch 13, a transmission output control circuit 14, an ear receiver switch 15 for turning ON and OFF a voice signal from the RF receiver to an ear receiver 17, a microphone switch 16 for turning ON and OFF a voice signal from a microphone 18 to the RF transmitter, a nonvolatile backup memory 31 for storing therein channel connection information, and so on.
A detachable power supply battery 3 supplies power through its battery contacts 39 to the main and secondary CPUs 1 and 2 and also to the RF receiver and transmitter. More in detail, the power supply from the power supply battery 3 to the main CPU 1 is carried out under the control of a power state signal 33 issued from the secondary CPU 2 to the main CPU 1.
That is, when the power supply battery 3 is connected for the first time, the secondary CPU 2 turns OFF the power state signal 33 and gets ready for an input from the electronic power supply switch 35. The main CPU 1 is not supplied with power from the power supply battery 3 under the control of the power state signal 33 and therefore circuits of the cellular telephone mobile station to be controlled by the main CPU 1 are all put in their OFF state.
When the electronic power supply switch 35 is now turned ON, this causes the secondary CPU 2 to turn ON the power state signal 33, whereby the main CPU 1 is activated so that a control information signal 23 issued from the main CPU 1 causes the secondary CPU 2 to be activated.
Thus, the cellular telephone mobile station is put in its idle mode so that, when originating a call or receiving a call, the mobile station is put in its conversation mode, during which, even when the power supply battery 3 is exchanged, the mobile station can keep a radio-link, which will be detailed later.
Next, the radio-link continuity keeping operation when the power supply battery 3 is exchanged in the conversation mode will be explained by referring to FIGS. 4 and 5.
In FIG. 5, the main and secondary CPUs 1 and 2 are both in their operational mode in the conversation mode (step 41). The main CPU 1, when receiving a channel information, operates the RF receiver, RF transmitter, channel supervisory signal receive/send circuit 11, channel selector 12, RF transmitter operation switch 13, transmission output control circuit 14, ear receiver switch 15 and microphone switch 16 (step 42).
At this time, if the power supply battery 3 is exhausted, a low voltage alarm is issued (step 43) and the power supply battery 3 is detached from the telephone set (step 44), then this causes the main CPU 1 to stop its operation with the channel information being stored in the backup memory 31, which results in that the secondary CPU 2 similarly stops its operation (step 45).
When a new power supply battery 3 is set (step 46) in place of the old one, as in the aforementioned initial mode, the secondary CPU 2 turns OFF the power state signal 33 to be sent to the main CPU 1 and gets ready for an input from the electronic power supply switch 35, whereas the main CPU 1 is not supplied with power from the power supply battery 3 under the control of the turned-OFF power state signal 33 (steps 47 and 48).
When the electronic power supply switch 35 is turned ON (step 49), the secondary CPU 2 turns ON the power state signal 33 to activate the main CPU 1 (step 50), so that the main CPU 1 outputs the control information signal 23 to start the secondary CPU 2 (step 51). Subsequently, the main CPU 1 turns ON only the RF receiver and turns OFF the RF transmitter, channel supervisory signal receive/send circuit 11, channel selector 12, RF transmitter operation switch 13, transmission output control circuit 14, ear receiver switch 15 and microphone switch 16 to abort the voice channel (step 52), which results in that the mobile station is put in the idle mode (step 53).
In the present example, there is provided a timer which measures an elapsed time after the power supply battery 3 is removed to turn OFF the main CPU until the electronic power supply switch 35 is turned ON to restart the main CPU 1, that is, which measures a time during which the main CPU 1 is not supplied with power. Therefore, when the measured elapsed time is shorter than a predetermined value, the channel can be restored on the basis of the channel information stored in the backup memory 31.
However, such prior art cellular telephone mobile station as mentioned above has had a problem that, in order to exchange a battery during telephone conversation, without losing the radio-link, the electronic power supply switch 35 should be turned ON in a predetermined time period after removal of the old power supply battery and insertion of a new one.